University of Groningen

PET Imaging of Mild Traumatic Brain Injury and Whiplash Associated DisorderVállez García, David

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David Vállez García, Andreas Otte, Antoon TM Willemsen,Rudi AJO Dierckx, Janine Doorduin, Gert Holstege

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AbstractWhiplash Associated Disorder (WAD) in one of the most frequent consequences of motor vehicle accidents. While initial symptoms resolve within a few weeks in many cases, some patients develop persistent symptoms that include pain, headache, visual, and/or psychological disturbances. Although there is evidence supporting tissue lesion and central hyperexcitability, the pathophysiology is not well understood. In the current study, possible alterations in the regional cerebral blood flow (rCBF) were explored with PET imaging. Twelve female patients diagnosed with WAD grade I/II were included 5±2 years after the accident, in addition to eight healthy matched volunteers. PET scans (Ecat HR+, Siemens) were acquired after injection of 500 MBq [15O]H2O for rCBF measurement. During acquisitions the volunteers received a non-painful electrical stimulation of the neck. Sensitivity thresholds were individually determined. Four conditions were used: rest state, placebo-like state (current was expected but not generated), stimulation above perception threshold, and stimulation below pain or muscular contraction. These conditions were repeated three times, resulting in twelve scans. All participants completed a neurological interview, the Hospital Anxiety and Depression Scale, the Neck Disability Index (NDI), the Whiplash Disability Questionnaire, and rated pain on the visual analogue scale. Voxel-based analysis was performed on the scans with SPM8 in combination with SwE toolbox to account for repeated measurements. Level of significance was set to p<0.005 uncorrected, with an extent threshold of 100 voxels. Correlations between the rCBF of WAD patients in the significant clusters and the scores from questionnaires were analyzed using the Generalized Estimating Equations model in SPSS, with p<0.05 considered significant. In all the questionnaires WAD patients scored higher (p<0.001) than healthy volunteers. No significant differences in rCBF were found between conditions. In WAD patients, compared with healthy controls, a significant increase in the rCBF was found in the right superior parietal gyrus (Z=2.96±0.30). In addition, a decreased rCBF was found in the left insula (Z=3.03±0.39), right insula (Z=3.06±0.40), and right thalamus (Z=2.94±0.27). Within the WAD group, a negative association (p<0.009) was found between the NDI scores and the rCBF. WAD symptoms might be the result of a mismatch between the proprioceptive information from the cervical spinal cord and the information integrated in regions such as mesencephalon, thalamus and insula. However, further investigation of the functional brain alterations present in WAD patients must be performed for a better understanding of the pathophysiology.

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IntroductionWhiplash trauma is one of the most frequent consequences of motor vehicle related accidents. It is estimated to have a yearly cost in Europe of at least €10 billion1 and $29 billion in the United States,2 affecting about 300 per 100,000 persons per year in North America and Western European countries.3 While in many cases the initial symptoms resolve within few weeks after the accident, approximately half of whiplash injured individuals will develop persistent symptoms.4 This heterogeneous group of symptoms is generally defined as Whiplash-associated disorder (WAD),5 and include pain in the neck and headache as the most frequent symptoms, followed by interscapular and temporomandibular pain, paresthesia in arms and hands, dizziness, visual and psychological disturbances.6

While there is evidence supporting lesion of various tissues in WAD, mainly concerning the zygapophysial (facet) joints, most of these injuries are undetected by conventional imaging techniques.7 Radiography, computed tomography (CT), and magnetic resonance imaging (MRI) are inconclusive for the prognosis of WAD.8 Aside from the use of standard imaging techniques for clinical diagnosis, the use of functional neuroimaging techniques such positron emission tomography (PET) and single-photon emission computed tomography (SPECT) can help to understand the underlying mechanism of WAD. Otte et al.9,10 performed a series of PET and SPECT studies in over 500 whiplash patients at rest using different tracers [99mTc]-hexamethyl propylene amine oxime (HMPAO), [99mTc]-ethylene biyldicysteinate dimer (ECD), and [18F]-fluorodeoxyglucose (FDG). Hypoperfusion and hypometabolism in the posterior parietal occipital cortex was observed in many of the patients as compared with healthy control. Similar findings were obtained recently in a PET study that measured the regional cerebral blood flow (rCBF) by means of [15O]H2O. Moreover, elevated rCBF was found bilaterally in the posterior parahippocampal, posterior cingulate gyri, right medial prefrontal gyrus, and right thalamus.11 Other imaging studies support also these results, showing statistical significant reduced perfusion of the temporal lobe in WAD patients,12 and non-significant (uncorrected voxel level of p=0.001) small regions with lower rCBF at the left temporoparietal, and right temporal region.13 However, other studies did not obtain similar results,14,15 maybe as consequence of the presence of important biases in the study design, e.g. control group composed mainly of melanoma patients.

The current study was design to address three main objectives. First, it intends to replicate the results of previous experiment that shown alterations in the rCBF in the posterior parietal, temporal and occipital lobe, hypothesized to be related with nociceptive afferents causing increased levels of vasopeptide

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induced vasoconstriction.16,17 Secondly, to explore our hypothesis according to which WAD symptoms may be induced by a mismatch in the midbrain, periaqueductal gray (PAG) and adjoining regions, between the ascending information from cervical structures via the upper cervical cord to the mesencephalon, and the information from the vestibular and visual systems.18 And finally, to test if non-painful stimuli in the neck region of WAD patients was altered due to an ongoing process of central hyperexcitability.19

MethodsParticipantsTwelve WAD patients (grade one or two,5,20 between 2 and 10 years after the accident) and eight healthy volunteers, all females, were recruited via advertisement in public buildings, local newspapers and radio, national association of whiplash patients (Whiplash Stichting Nederland), and the Royal Dutch Society for Physical Therapy. Screening procedures included telephone questioning and brief interview. If the volunteer was considered electable, a neurological interview was scheduled for a final screening. Specific exclusion criteria for patients were loss of consciousness at the accident, neurological symptoms, and pain not related to WAD. Exclusion criteria for both WAD patients and healthy volunteers were current depression, anxiety, or other psychiatric disorder, organic brain disorder, somatic disease, left-handedness, substance abuse, pregnancy, and body mass index (BMI) ≥ 30 kg/m2.

All participants were asked to refrain from analgesics and anti-inflammatory drugs one to three days prior to scanning; from tobacco, alcohol and caffeine 12 h before, and from food 3 h before the PET scan. According to the Declaration of Helsinki, all participants gave written informed consent. The internal ethics committee of the University Medical Center of Groningen approved the experimental.

PET proceduresDuring the whole procedure, the room lights were maintained at low intensity. The skin of the back part of the neck was rinse with alcohol, and disposable auto-adhesive skin electrodes (Model ST5090 5×9 cm, Axelgaard Manufacturing Co., USA) were placed at both sides of the neck, approximately at the level of the second and sixth cervical spinous process.

Four different conditions were used during the experiment, which were repeated three times resulting in a total of twelve scans per subject:

1. Rest state: no stimulation.

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2. Low stimulation: 15% above the perception threshold.

3. High stimulation: 15% below observable muscular contraction or pain threshold.

4. Placebo-like stimulation: the participant was informed that will receive an electrical stimulation, below her perception level; but the device did not delivered any current.

The order of the sequences was modified between participants, keeping constant the rest scan as the 1st, 5th, and 9th scan. The stimulation consisted on a non-painful electrical constant current, delivered with the Digitimer DS7A device in combination with the stimulator DG2A (Digitimer Limited, UK), using a biphasic pulse, train repetition of 50 Hz, and 100 µs pulse duration. These parameters were selected based on a pilot test performed in a small group of healthy volunteers independent from this study (n=5). These values were found to allow an acceptable current range (mA) to define the thresholds, without apparent discomfort in the participant. Before the first PET scan, with the participant lying in the scanner, individual thresholds were determined by slow increase of the mA. First, the participant was asked to notify the researcher when the current was clearly perceived (lower threshold, considered as 0%). Then, the highest threshold (100%) was set when the participant notifies that the current was painful or unpleasant, or the researcher detected a clear muscular contraction. This procedure was repeated three times, with an interval of 1–2 min between trials. The average value of these thresholds was calculated, and used during the scan to define the low (15%) and high (85%) stimulation conditions. Before injection of the radiotracer the participant was informed about the condition that was going to be delivered as ‘rest’, ‘low’ for the placebo, ‘medium’ for the low stimulation (15%), and ‘high’ for the higher stimulation (85%). The device was turned on for all the conditions, except for rest condition. Immediately after each scan, the device was turned off, and the subject was allowed to open the eyes.

Each of the twelve PET scans was made in 3D mode (63 planes; axial field of view of 15.5 cm) using an Ecat Exact HR+ camera (CTI/Siemens, USA) with a spatial resolution of 4–5 mm full width at half maximum in all three directions. For the scan, the radiotracer [15O]H2O was used as a measure of regional cerebral blood flow (rCBF). Per scan, 500 MBq of activity dissolved in 32 mL of 0.9% saline were administered intravenously into the right forearm at 8 mL/sec. After injection of the radiotracer, data were collected for 120 sec. Consecutive scans were made with intervals of 10–15 min. The participants were asked to keep their eyes closed during the scanning period, and their head was maintained in position using a head-restraining adhesive

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band. A scan specific calculated attenuation correction was performed to minimize inter-scan displacement induced variance.21 Data acquisition was reconstructed using a filtered back projection procedure, corrected for background radiation, and summed to obtain a final 120 sec rCBF image.

Subjective ratingsDuring the neurological interview performed previous to the scan, all participants completed the Hospital Anxiety and Depression Scale (HADS),22,23 rated levels of pain between 0 and 10 (none to worst imaginable) on visual analogue scale (VAS), and the Neck Disability Index (NDI).24–26 An in-house translation of the Whiplash disability questionnaire (WDQ)27 was also provided.

Neuroimaging analysisPET images were processed using the statistical parametric mapping (SPM8) software (Wellcome Department of Cognitive Neurology, London, United Kingdom) in combination with the Sandwich Estimator v1.2.1 (SwE) toolbox to account for the repeated measures.28 Images were first aligned between acquisitions for each subject, and then normalized to the Montreal Neurological Institute’s (MNI) stereotactic template. Images were masked for the whole brain image and then smoothed using a 12 mm Gaussian kernel. PET data was statistically evaluated with a small sample adjustment ‘type C2’ and ‘approximate III’ estimation for the degrees of freedom. A factorial design was used with group, conditions, and their interactions as factors. Differences in global blood flow were corrected using the ANCOVA between-subject and within-subject method.29 Level of significance was set to p<0.005 uncorrected, with an extent threshold of 100 voxels. Anatomical localization of the results was aided by the Hammers atlas.30,31

In the WAD group, to explore the association between the altered rCBF and the symptoms, the statistical significant clusters obtained from the voxel-based analysis in SPM were divided according to the Hammers atlas, creating independent anatomical regions. The mean rCBF value for each of these regions was extracted from the original images and corrected for the mean whole brain uptake. These values were analyzed together with the scores obtained from the self-questionnaires (VAS, WDQ, NDI and HADS) using IBM SPSS Statistics 22 (SPSS Inc. Chicago, The United States). The Generalized Estimating Equations (GEE) model32 was used to account for multiple measures per subject and brain regions (clusters), with an auto-regressive correlation matrix. The age and BMI were also included in the model as covariates. No correction for multiple comparisons was applied, and p<0.05 were considered statistically significant.

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ResultsGeneral statisticsAll the participants were females, with a mean (± SD) age of 28±8 years for the control group (n=8), and 33±7 years for the patient group (n=12). No statistical differences were found between groups in age (p=0.15) or BMI (p=0.40). WAD patients suffered the accident 5±2 years before the study, and scored statistically higher for all the subjective ratings compared with the healthy volunteers (p<0.001). When comparing the sensitivity threshold, the highest threshold of the WAD patients was 83% of the one in healthy subjects (p=0.033), but not differences was observed in the lowest threshold between groups. More details can be found in Table 1.

Regional cerebral blood flowNo statistically significant differences were found between any of the experimental conditions in the voxel-based analysis (i.e.: rest, placebo or electrical stimulation of the neck), when the groups were compared independently or combined. However, statistically significant differences in the rCBF were found in several brain regions of WAD patients when this group was compared with the healthy volunteers (Table 2, Figure 1 and Figure 2). The peak voxels with increased rCBF on WAD patients was found in the right superior parietal gyrus (Z-score=3.76, x,y,z=13, -58, 17); while the peaks of decreased rCBF were detected in the right insula (Z-score=4.28, x,y,z=35, 0, -19), left insula (Z-score=4.23, x,y,z=-35, 22, -7), and right thalamus (Z-score=3.64, x,y,z=5, -12, 3).

Table 1. Differences between patients and control volunteers

Controls(n=8)

Patients(n=12) p-values

Age 28 ± 8 33 ± 7 0.150BMI 25 ± 3 24 ± 3 0.401VAS 0 6 ± 2 <0.001*WDQ 0 63 ± 19 <0.001*NDI 0 24 ± 6 <0.001*HADS 0 10 ± 6 <0.001*Lowest Threshold 39 ± 8 33 ± 8 0.147Highest Threshold 72 ± 10 60 ± 13 0.033*

Mean values (±SD). BMI: body mass index, VAS: pain measured with visual analog scale, HADS: Hospital Anxiety and Depression Scale, NDI: Neck Disability Index, WDQ: Whiplash Disability Questionnaire. * p<0.05

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Decreased rCBFIncreased rCBF

Figure 1. SPM results of the voxel-based analysis of [15O]H2O scans. The results shown regions with increased (left) and decreased (right) regional cerebral blood flood (rCBF) in Whiplash Associated Disorder patients as compared with healthy volunteers (p<0.005 uncorrected, extent threshold k=100 voxels)

Table 2. Alterations of the regional cerebral blood flow of in Whiplash-Associated disorder patients compared with healthy volunteers (p<0.005 uncorrected, extent threshold k=100 voxels)

Voxels in cluster Cluster Z-value Peak Z-value Peak x,y,z Peak location

Healthy<WAD116 2.96±0.30 3.76 13 -58 17 Superior parietal gyrus right

Healthy > WAD152 3.06±0.40 4.28 35 0 -19 Insula right107 3.03±0.39 4.23 -33 22 -7 Insula left147 2.94±0.27 3.64 5 -12 3 Thalamus right

Peak voxel coordinates are in MNI space. Anatomical location according to Hammer’s brain atlas.

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Insula

Insula Insula

Insula Superior parietal gyrus

Thalamus

Thalamus

Superior parietal gyrus

Decreased rCBF Increased rCBF

Figure 2. Voxel-based analysis of [15O]H2O scans. The results shown some of the most significant regions with decreased or increased regional cerebral blood flood (rCBF) in Whiplash Associated Disorder patients as compared with healthy volunteers (p<0.005 uncorrected, extent threshold k=100 voxels)

Association between subjective ratings and altered rCBFWithin the WAD group, there were significant positive correlations (Table 3) between age and BMI (r=0.71, p=0.01), NDI scores and VAS pain ratings (r=0.70, p<0.010), NDI and WDQ (r=0.71, p=0.01), HADS and WDQ (r=0.83, p=0.001), and HADS and NDI (r=0.65, p=0.022). The rCBF values obtained from the four statistically significant clusters found previously in the voxel-based analysis were included in the GEE model as the outcome variable. The subjective ratings were included in the model as predictors, with the age and the BMI as covariates (Table 4). Only a positive association between the NDI score and the rCBF values extracted from the clusters was found in the analysis (B=0.004±0.001, 95% CI [0.001; 0.006], p<0.009).

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DiscussionThe present study was designed with the purpose to address three main research questions. First, the validation of the results showing hypoperfusion in the posterior parietal, temporal and occipital cortex, reported previously by Otte et al.,9,10 and Linnman et al.11 Secondly, to evaluate our hypothesis according to which a dysfunction in midbrain structures is behind most of the symptoms found in chronic WAD patients, with the PAG acting as a key player. And finally to explore the ongoing process of central hyperexcitability in WAD patients, comparing rest state brain perfusion with the expected changes in rCBF consequence of a non-painful stimulation. In this context, the increased rCBF found in the right superior parietal gyrus of the WAD group as compared with the healthy volunteers, seems to support that the parietal cortex is some how involved in the symptoms related with the

Table 3. Pearson correlations within the WAD patient groupAge Time BMI VAS WDQ NDI HADS

Age 1 0.056 0.707 -0.520 -0.406 -0.341 -0.148p=0.863 p=0.010 p=0.083 p=0.190 p=0.278 p=0.646

Time 1 -0.448 -0.362 -0.241 -0.207 -0.369p=0.144 p=0.248 p=0.450 p=0.518 p=0.238

BMI 1 -0.205 -0.321 -0.195 -0.099p=0.523 p=0.308 p=0.543 p=0.759

VAS 1 0.521 0.705 0.355p=0.082 p=0.010 p=0.257

WDQ 1 0.710 0.835p=0.010 p=0.001

NDI 1 0.6500.022

BMI: body mass index, VAS: visual analogue scale, WDQ: Whiplash disability questionnaire, NDI: neck disability index, HADS: hospital anxiety and depression scale

Table 4. Association between subjective ratings and alterations in the regional cerebral blood flow (rCBF) of WAD patients

CIB ± SE Lower Upper p-value

(Intercept) 1.056 ± 0.024 1.009; 1.102 <0.001Visual Analogue Scale (VAS) 0.004 ± 0.005 -0.007; 0.014 0.477Whiplash Disability Questionnaire (WDQ) -0.001 ± 0.001 -0.003; 0.001 0.282Neck Disability Index (NDI) 0.004 ± 0.001 0.001; 0.006 0.009Hospital Anxiety and Depression Scale (HADS) 0.003 ± 0.003 -0.003; 0.008 0.365

SE: Standard Error; CI: 95% confidence interval

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chronic WAD patients. In addition, we consider that the decreased rCBF detected bilaterally in the insula and in the right thalamus of the WAD group support the hypothesis of a misbalance in the interoceptive sensory system, even when no alterations of the perfusion were detected in the PAG with the current study design. And finally, no differences were found in the regional brain perfusion as consequence of the different levels of electrical non-painful stimulation

There is an increasing evidence for a process of central hyperexcitability in chronic WAD patients, resulting in widespread lowered pain thresholds.19 In our study, volunteers were exposed to four different experimental conditions: absence of stimulation, placebo stimuli, and low/high non-painful stimulation of the neck. The first condition, without any stimulation, was intended to replicate the experimental setup presented by Linnman et al.11 While the placebo condition was introduced to assess the presence of altered brain perfusion patterns in relation with “beliefs and expectations” of WAD patient.33,34 And finally, the use of two different intensities levels of the electrical current stimuli pursued the exploration of rCBF changes in a non-painful condition. Contrary to our prior expectations, no alterations were observed in the rCBF as consequence of the different stimulation conditions, in either healthy or WAD patients. The absence of changes in the rCBF in regions such as the primary and secondary somatosensory cortex may be a consequence of the discrepancies generated by the lack of individual MRI scans to perform a more accurate process of spatial normalization of the scans; or may just reflect that the non-painful stimulations used in the present study design were not sufficient to induce substantial alterations in the rCBF that could be detected by the PET camera. However, a statistically significant lower tolerance to the electrical stimulation of the neck was found in the WAD patients when compared with the healthy volunteers, achieving unpleasant or painful feelings at lowest intensities of electrical current. These results support the idea that chronic WAD patients had alterations of their sensitivity thresholds, which is in agreement with the results presented in a recent meta-analysis of central hyperexcitability in chronic WAD patients.19

Furthermore, when the rCBF of WAD patients was compared with healthy volunteers, brain regions commonly involved in the process of acute painful stimuli such as the insular cortex and the thalamus35,36 were found to exhibit alteration in its perfusion. In this sense, it is of special interest the decrease in rCBF that was observed bilaterally in the insula. Although no changes in perfusion of WAD patients were reported previously in this region,9–11,13,14 the insula it is been recognized as the primary reception area for the interoceptive sensory information, and its critical for the process of emotional feelings.37 Moreover, in a recent study performed with the radioligand [11C]GR205171,38

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a significant lower neurokinin 1 (NK1) receptor availability was found in the left insula of chronic WAD patients, as well as in the frontal and cingulate cortex, hippocampus, amygdala, and the PAG. The NK1 receptors are widely distributed throughout the brain, and are the primary receptor of the neuropeptide “substance P” that modulates pain.39

The increased rCBF found in the right superior parietal gyrus of the females chronic WAD groups seems to support the relevance of this region in the pathophysiology of WAD, as this changes are similar to those previously reported by Otte et al.,9–10 and Linnman et al.,11 involving parietal, temporal and occipital cortex. However, their results showed a hypoperfusion in those regions, while in the present study an increased rCBF was observed. This discrepancy in the direction of the results may be consequence of an error in the calculation of the global mean uptake within SPM software (unpublished work). Moreover, alterations in the rCBF shown by Linnmann et al. in the parahippocampal region or the cingulate gyrus, were not replicated in this study. These difference can be explained also by the discrepancies that arise when the data is analyzed in the MNI space, as is the case of SPM, but the results are reported using the Tailarach space.40 When the MNI peak coordinates, originally reported as parahippocampal region (18 -44 8), are explored using the Hammer atlas, the closest regions identified was the superior parietal gyrus. Independently of the final label used to classify the anatomical location of this region, in the present study these coordinates were found to be closer to the increased rCBF in found in WAD patients (i.e. right superior parietal gyrus).

Standard imaging techniques such as radiography, CT and MRI seem to be inconclusive for the prognosis of the symptoms after a whiplash trauma,8 and most of the current efforts are directed to understand the role of the tissue damage,7 and the processes involved in the transition from acute to chronic WAD.41 However, not much is known about how it is that reasonable simple accidents, often at rear-end low speed collisions, can induce brain processes such as the central hyperexcitability found in chronic WAD patients. We had hypothesized18 that the missing key for the understanding of the underlying pathophysiology in WAD is the close interaction between neck and midbrain thorough the spino-PAG and spino-thalamic fibers originated from the C1-C3 spinal segments.42,43 These neurons are distributed throughout lamina VI-VIII, with a specific cluster of them located in the ventrolateral horn.44 In addition, the trigeminocervical complex, constituted by the trigeminal nucleus caudalis and C1-C2 dorsal horn, maintains projections to the PAG and is known to be involved in the development of migraine and headaches.45 All these ascending pathways converge in the neurons located at the PAG and adjoining regions, basic for the normal function of multiple processes. In

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WAD patients, the PAG and adjoining regions have been shown to express lower NK1 receptors,38 and undergo gray matter changes associated with the development of headache.46 In the present study no alteration in the rCBF of the PAG were detected. Adequate registration of the brainstem structures in our study using the automated method implemented in SPM8 was most probably suboptimal, especially in the absence of individual MRI images to be used in a more accurate process.47 However, the alterations detected in other brain regions related with interoceptive and pain processing pathways are appealing (i.e. bilaterally in the insula, and right thalamus).

Moreover, it seems to be an association between the rCBF values and the severity of the condition assessed by the NDI scores. Although these results must be taken with caution due to the small number of subjects included in the study these findings are of interest in the design of future experiments.

As mentioned before, the present study posses some limitations in its design. The most important one is that current results are drawn from a relative small sample size, compose only by females. While this is an important factor when interpreting the results related with the association of subjective scorings and the rCBF at different brain locations, we must consider that it has a relative lower relevance in the results obtained in the group comparison of rCBF. Since no differences were found between the presented stimuli, the comparison between chronic WAD patients and healthy volunteers was performed with 12 repetitions of the [15O]H2O scan per subject. These repeated measurements are important to control for within-subject variability, and strength the results of the analysis thanks to the use of advanced statistical methods such as those implemented in the “sandwich estimator” toolbox. Finally, the absence of individual MRI acquisitions may have influence in the accuracy of the registration procedure, making more difficult the precise exploration of rCBF changes in some regions such as the brainstem.

ConclusionWAD symptoms might be the result of a mismatch between the proprioceptive information from the cervical spinal cord and the information integrated in regions such as thalamus and insula. Further investigation of the functional brain alterations present in WAD patients must be performed for a better understanding of its pathophysiology.

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References1. Report EW. Reining in Whiplash Executive Director.; 20052. Freeman MD, Croft AC, Rossignol AM, Weaver DS, Reiser M. A review and methodologic critique of the

literature refuting whiplash syndrome. Spine (Phila Pa 1976). 1999;24(1):86-963. Holm LW, Carroll LJ, Cassidy JD, et al. The burden and determinants of neck pain in whiplash-associated

disorders after traffic collisions: results of the Bone and Joint Decade 2000-2010 Task Force on Neck Pain and Its Associated Disorders. Spine (Phila Pa 1976). 2008;33(4 Suppl):S52-S59. doi:10.1097/BRS.0b013e3181643ece

4. Carroll LJ, Holm LW, Hogg-Johnson S, et al. Course and prognostic factors for neck pain in whiplash-associated disorders (WAD): results of the Bone and Joint Decade 2000-2010 Task Force on Neck Pain and Its Associated Disorders. Spine (Phila Pa 1976). 2008;33(4 Suppl):S83-S92. doi:10.1097/BRS.0b013e3181643eb8

5. Spitzer WO, Skovron ML, Salmi LR, et al. Scientific monograph of the Quebec Task Force on Whiplash-Associated Disorders: redefining “whiplash” and its management. Spine (Phila Pa 1976). 1995;20(8 Suppl):1S - 73S

6. Sterner Y, Gerdle B. Acute and chronic whiplash disorders--a review. J Rehabil Med. 2004;36(5):193-209; quiz 210. doi:10.1080/16501970410030742

7. Curatolo M, Bogduk N, Ivancic PC, McLean SA, Siegmund GP, Winkelstein BA. The Role of Tissue Damage in Whiplash-Associated Disorders. Spine (Phila Pa 1976). 2011;36(25):S309-S315. doi:10.1097/BRS.0b013e318238842a

8. Williams M, Williamson E, Gates S, Lamb S, Cooke M. A systematic literature review of physical prognostic factors for the development of Late Whiplash Syndrome. Spine (Phila Pa 1976). 2007;32(25):E764-E780. doi:10.1097/BRS.0b013e31815b6565

9. Otte A, Mueller-Brand J, Fierz L. Brain SPECT findings in late whiplash syndrome. Lancet. 1995;345(8963):1513-1514

10. Otte A, Mueller-Brand J, Nitzsche EU, Wachter K, Ettlin TM. Functional brain imaging in 200 patients after whiplash injury. J Nucl Med. 1997;38(6):1002

11. Linnman C, Appel L, Söderlund A, et al. Chronic whiplash symptoms are related to altered regional cerebral blood flow in the resting state. Eur J Pain. 2009;13(1):65-70. doi:10.1016/j.ejpain.2008.03.001

12. Lorberboym M, Gilad R, Gorin V, Sadeh M, Lampl Y. Late whiplash syndrome: correlation of brain SPECT with neuropsychological tests and P300 event-related potential. J Trauma. 2002;52(3):521-526

13. Sundström T, Guez M, Hildingsson C, Toolanen G, Nyberg L, Riklund K. Altered cerebral blood flow in chronic neck pain patients but not in whiplash patients: a 99mTc-HMPAO rCBF study. Eur Spine J. 2006;15(8):1189-1195. doi:10.1007/s00586-005-0040-5

14. Bicik I, Radanov BP, Schäfer N, et al. PET with 18fluorodeoxyglucose and hexamethylpropylene amine oxime SPECT in late whiplash syndrome. Neurology. 1998;51(2):345-350

15. Radanov BP, Bicik I, Dvorak J, Antinnes J, von Schulthess GK, Buck A. Relation between neuropsychological and neuroimaging findings in patients with late whiplash syndrome. J Neurol Neurosurg Psychiatry. 1999;66(4):485-489. doi:10.1136/jnnp.66.4.485

16. Moskowitz M a, Buzzi MG. Neuroeffector functions of sensory fibres: implications for headache mechanisms and drug actions. J Neurol. 1991;238 Suppl :S18-S22

17. Otte A. Functional neuroimaging in whiplash injury. Eur J Pain. 2012;16(1):160-161; author reply 162-163. doi:10.1016/j.ejpain.2011.08.002

18. Vállez García D, Dierckx RAJO, Otte A, Holstege G. Whiplash, Real or Not Real? A Review and New Concept. In: Dierckx RAJO, Otte A, de Vries EFJ, van Waarde A, Leenders KL, eds. PET and SPECT in Neurology. Vol Berlin, Heidelberg: Springer Berlin Heidelberg; 2014:947-963. doi:10.1007/978-3-642-54307-4

19. Stone AM, Vicenzino B, Lim ECW, Sterling M. Measures of central hyperexcitability in chronic whiplash associated disorder - A systematic review and meta-analysis. Man Ther. 2013;18(2):111-117. doi:10.1016/j.math.2012.07.009

20. Institute for Quality in Healthcare CBO. Richtlijn Diagnostiek En Behandeling van Mensen Met Whiplash Associated Disorder I / II. Utrecht, The Netherlands; 2008

Altered Regional Cerebral Blood Flow in Chronic Whiplash Associated Disorder

163

7

21. Reinders AATS, Willemsen ATM, Georgiadis JR, Hovius M, Paans AMJ, den Boer JA. Interscan displacement-induced variance in PET activation data is excluded by a scan-specific attenuation correction. Neuroimage. 2002;17(4):1844-1853

22. Zigmond AS, Snaith RP. The hospital anxiety and depression scale. Acta Psychiatr Scand. 1983;67(6):361-370

23. Spinhoven P, Ormel J, Sloekers PP, Kempen GI, Speckens AE, Van Hemert AM. A validation study of the Hospital Anxiety and Depression Scale (HADS) in different groups of Dutch subjects. Psychol Med. 1997;27(2):363-370

24. Vernon H, Mior S. The Neck Disability Index: a study of reliability and validity. J Manipulative Physiol Ther. 1991;14(7):409-415

25. Vernon H. The Neck Disability Index: state-of-the-art, 1991-2008. J Manipulative Physiol Ther. 2008;31(7):491-502. doi:10.1016/j.jmpt.2008.08.006

26. MacDermid JC, Walton DM, Avery S, et al. Measurement properties of the neck disability index: a systematic review. J Orthop Sports Phys Ther. 2009;39(5):400-417. doi:10.2519/jospt.2009.2930

27. Pinfold M, Niere KR, O’Leary EF, Hoving JL, Green S, Buchbinder R. Validity and internal consistency of a whiplash-specific disability measure. Spine (Phila Pa 1976). 2004;29(3):263-268

28. Guillaume B, Hua X, Thompson PM, Waldorp L, Nichols TE. Fast and accurate modelling of longitudinal and repeated measures neuroimaging data. Neuroimage. 2014;94:287-302. doi:10.1016/j.neuroimage.2014.03.029

29. Penny W, Friston K, Ashburner J, Kiebel S, Nichols T. Statistical Parametric Mapping: The Analysis of Functional Brain Images. Vol 1st ed. (Friston KJ, Ashburner JT, Kiebel S, Nichols T, Penny WD, eds.). Academic Press; 2006

30. Hammers A, Allom R, Koepp MJ, et al. Three-dimensional maximum probability atlas of the human brain, with particular reference to the temporal lobe. Hum Brain Mapp. 2003;19(4):224-247. doi:10.1002/hbm.10123

31. Gousias IS, Rueckert D, Heckemann RA, et al. Automatic segmentation of brain MRIs of 2-year-olds into 83 regions of interest. Neuroimage. 2008;40(2):672-684. doi:10.1016/j.neuroimage.2007.11.034

32. Hardin JW, Hilbe JM. Generalized Estimating Equations. Vol Second. Chapman & Hall/CRC; 201233. Carroll LJ, Holm LW, Ferrari R, Ozegovic D, Cassidy JD. Recovery in whiplash-associated disorders: do

you get what you expect? J Rheumatol. 2009;36(5):1063-1070. doi:10.3899/jrheum.08068034. Bostick GP, Carroll LJ, Brown CA, Harley D, Gross DP. Predictive capacity of pain beliefs and catastrophizing

in Whiplash Associated Disorder. Injury. 2013;44(11):1465-1471. doi:10.1016/j.injury.2012.10.00735. Apkarian AV, Bushnell MC, Treede RD, Zubieta J-K. Human brain mechanisms of pain perception and

regulation in health and disease. Eur J Pain. 2005;9(4):463-484. doi:10.1016/j.ejpain.2004.11.00136. Duerden EG, Albanese MC. Localization of pain-related brain activation: a meta-analysis of neuroimaging

data. Hum Brain Mapp. 2013;34(1):109-149. doi:10.1002/hbm.2141637. Gasquoine PG. Contributions of the insula to cognition and emotion. Neuropsychol Rev. 2014;24(2):77-87.

doi:10.1007/s11065-014-9246-938. Linnman C, Appel L, Furmark T, et al. Ventromedial prefrontal neurokinin 1 receptor availability is reduced

in chronic pain. Pain. 2010;149(1):64-70. doi:10.1016/j.pain.2010.01.00839. Hietala J, Nyman MJ, Eskola O, et al. Visualization and quantification of neurokinin-1 (NK1) receptors in

the human brain. Mol Imaging Biol. 2005;7(4):262-272. doi:10.1007/s11307-005-7001-640. Brett M, Johnsrude IS, Owen AM. The problem of functional localization in the human brain. Nat Rev

Neurosci. 2002;3(3):243-249. doi:10.1038/nrn75641. Sterling M, McLean S a, Sullivan MJL, Elliott JM, Buitenhuis J, Kamper SJ. Potential processes involved

in the initiation and maintenance of whiplash-associated disorders: discussion paper 3. Spine (Phila Pa 1976). 2011;36(25 Suppl):S322-S329. doi:10.1097/BRS.0b013e318238853f

42. Mouton LJ, Klop E, Holstege G. Lamina I-periaqueductal gray (PAG) projections represent only a limited part of the total spinal and caudal medullary input to the PAG in the cat. Brain Res Bull. 2001;54(2):167-174

43. Klop EM, Mouton LJ, Holstege G. Less than 15% of the spinothalamic fibers originate from neurons in lamina I in cat. Neurosci Lett. 2004;360(3):125-128. doi:10.1016/j.neulet.2004.02.047

Chapter 7

164

44. Mouton LJ, Eggens-Meijer E, Klop EM. The ventrolateral upper cervical cell group in cat projects to all rostrocaudal levels of the periaqueductal gray matter. Brain Res. 2009;1300:79-96. doi:10.1016/j.brainres.2009.08.088

45. Charbit AR, Akerman S, Goadsby PJ. Trigeminocervical complex responses after lesioning dopaminergic A11 nucleus are modified by dopamine and serotonin mechanisms. Pain. 2011;152(10):2365-2376. doi:10.1016/j.pain.2011.07.002

46. Obermann M, Nebel K, Schumann C, et al. Gray matter changes related to chronic posttraumatic headache. Neurology. 2009;73(12):978-983. doi:10.1212/WNL.0b013e3181b8791a

47. Limbrick-Oldfield EH, Brooks JCW, Wise RJS, et al. Identification and characterisation of midbrain nuclei using optimised functional magnetic resonance imaging. Neuroimage. 2012;59:1230-1238. doi:10.1016/j.neuroimage.2011.08.016